1. Field of the Invention
The present invention relates to a congestion control system, a congestion control method, a congestion control program, and a program recording medium, and, more particularly to a congestion control system, a congestion control method, a congestion control program, and a program recording medium for controlling traffic (communication amount) in an IP telephone system for providing a telephone communication service (VoIP (Voice over Internet Protocol)) through an IP network.
2. Description of the Related Art
When the IP telephone service for performing telephone communication through the IP network is realized, a CTI (Computer Telephony Integration) technique for integrating functions of a computer and a telephone is used. As a node (a component) configuring a service network on the IP network for providing such an IP telephone service, a CTI-GW (Gateway), a soft switch for performing line switching, and the like are used.
However, in the IP telephone service network (a telephone service network on the IP network), when a large number of calls to a specific incoming destination concentrate in the same period or when a large number of calls are originated from a specific outgoing source in the same period, it is likely that a large number of calls concentrate in a specific CTI-GW, congestion occurs, and a telephone communication function stops. When a large number of calls concentrate in the soft switch, it is likely that the soft switch itself stops. Besides, it is likely that functions of the entire IP telephone service stop.
For example, when control messages (call setting requests) are concentratedly originated from plural areas to a specific subscriber at a time, congestion occurs in a node that accommodates a user terminal of the subscriber. When congestion occurs in a certain node configuring the IP telephone service network, it is highly likely that the congestion sequentially propagates to adjacent nodes connected to the node to make the entire network unstable.
Therefore, for example, Japanese Patent Application Laid-Open No. 2004-88666 (hereinafter, Patent Document 1) proposes a mechanism for monitoring traffic (the number of calls) for each incoming destination per a unit time in order to eliminate occurring congestion or prevent occurrence of congestion for each node configuring an IP telephone service network and controlling, for the elimination of congestion or the prevention of occurrence of congestion, the number of connected calls to a specific incoming destination on the basis of density of the number of calls set in advance as a threshold.
The IP network that configures the service network for providing the telephone communication service on the IP network and provides the VoIP service has, in general, a configuration shown in FIG. 1.
FIG. 1 is a diagram showing an example of a configuration of the IP network for providing the VoIP service.
The IP network shown in FIG. 1 includes VoIP-U plane 90 that provides a user protocol between the IP network and a user terminal (a telephone terminal) and VoIP-C plane 10 that is a service network for an IP telephone for providing a control protocol for a VoIP call.
VoIP-U plane 90 is an IP network that connects user terminals 80 (80-1, 80-2, etc.) and formed by one layer of mesh-like topology. VoIP-U plane 90 is connected to a network of VoIP-C plane 10 through edge routers 15. Edge routers 15 are arranged to be distributed for each of areas decided in advance and connected to subscriber accommodation nodes CL5 11 (11-1, 11-2, etc.) for accommodating user terminals 80 (80-1, 80-2, etc.) in the area, respectively.
On the other hand, VoIP-C plane 10 is formed by topology of a route distributed system including two layers, i.e., a Local stage of plural subscriber accommodation nodes CL5 11 (11-1, 11-2, 11-3, etc.) and a Toll stage of relay nodes CL4 12 (12-1, 12-2, etc.) for relaying calls among subscriber accommodation nodes CL5 11 (11-1, 11-2, 11-3, etc.). Subscriber accommodation nodes CL5 11 and relay nodes CL4 12 cover user terminals in the areas, respectively.
Each of edge routers 15 is installed in association with each service provided on the IP network. When a request for a VoIP service is received from user terminal 80, VoIP-C plane 10 loads a control message for a call setting request from user terminal 80 on reception queue 16 for the VoIP service through edge router 15. According to the control message, VoIP-C plane 10 notifies the call setting request to subscriber accommodation node 11 (11-1) of the VoIP service network for accommodating user terminal 80 of the subscriber in the area. When VoIP-C plane 10 requests an IPTV service and other services, VoIP-C plane 10 is connected to C plane networks, which are service networks that realize the services, through edge routers 15 provided in association with the services, respectively.
When VoIP-C plane 10 performs network-to-network connection with PSTN (Public Switch Telephone Network) 50 and other networks 60, VoIP-C plane 10 connects certain relay node CL4 12 (12-1) of VoIP-C plane 10 and IGS (Interconnecting Gateway Switch) 51 of PSTN 50 and connects relay node CL4 12 (12-2) and gateways of other networks 60 to control incoming calls from PSTN 50 and other networks 60 or outgoing calls to PSTN 50 and other networks 60.
However, in the service network on the IP network in the past that provides a communication service such as the VoIP service, as shown in FIG. 1, various problems related to traffic on the communication service such as the VoIP service occur.
A first problem is that, when VoIP outgoing calls from plural user terminals 80 (80-1, 80-2, etc.) in a specific area are generated in a burst-like manner, it is highly likely that entire VoIP-C plane 10 for the VoIP service on the IP network falls into a congestion state.
This is because, when control messages for a large number of call setting requests are registered in reception queue 16 from edge router 15 in the area by burst traffic from plural user terminals 80 (80-1, 80-2, etc.) in the specific area, VoIP-C plane 10 does not have means for rejecting reception of the control messages for the call setting requests and repelling the control messages to user terminals 80 as request sources. As a result, a congestion state exceeding a processing ability of subscriber accommodation node CL5 11 (11-1) occurs. Consequently, the congestion spreads to relay node CL4 12 (12-1) connected to subscriber accommodation node CL5 11 (11-1). Moreover, the congestion state propagates to relay nodes CL4 12 and subscriber accommodation nodes CL5 11 beyond relay node CL4 12 (12-1) in succession. This leads to congestion in the entire network of VoIP-C plane 10.
Such a congestion problem in an originating system is a significant problem in the service network on the IP network that provides the VoIP service. A state of spread of congestion to the entire network of VoIP-C plane 10 is further explained with reference to FIG. 2.
FIG. 2 is a diagram for explaining a congestion spreading situation in an originating system node of the IP network that provides the VoIP service.
As described above, when control messages for call setting requests from edge router 15 in a specific area are registered in reception queue 16 as burst traffic at a time, subscriber accommodation node CL5 11-1 corresponding to edge router 15 attempts to process the large amount of call setting requests and falls into a congestion state. Subscriber accommodation node CL5 11-1 in the congestion state transmits processing requests for call setting to relay node CL4 12-1 one after another. Therefore, relay node CL4 12-1 adjacent to subscriber accommodation node CL5 11-1 also causes congestion.
Moreover, relay node CL4 12-1 transfers the processing requests for call setting to relay node CL4 12-2 adjacent thereto as a destination of routing to an incoming destination one after another. Therefore, relay node CL4 12-2 also causes congestion. Relay node CL4 12-2 transfers the processing requests for call setting to subscriber accommodation node CL5 11-2 as an incoming destination one after another. Therefore, subscriber accommodation node CL5 11-2 also causes congestion.
Furthermore, there is another problem. For example, in FIG. 2, as a routing method for transmitting control information for a certain area received by subscriber accommodation node CL5 11-2 to relay node CL4 12-2, a route bypass function of judging a congestion state of relay node CL4 12-2 and, when relay node CL4 12-2 is in a congestion state, automatically bypassing a route to another relay node CL4 12-4 is not provided. Therefore, because of a delay in a transfer operation between subscriber accommodation node CL5 11-2 and congesting relay node CL4 12-2, subscriber accommodation node CL5 11-2 also falls into a further congestion state. Similarly, in transfer of control information between relay nodes such as relay node CL4 12-2 and relay node CL4 12-1, a route bypass function of automatically bypassing a route to relay node CL4 12-3 without congestion is not provided. Therefore, because of a delay in a transfer operation between subscriber accommodation node CL5 11-2 and congesting relay node CL4 12-1, subscriber accommodation node CL5 11-2 falls into a further congestion state. Under the present situation, route bypassing in the VoIP network in the past is realized when the route bypassing is inputted by a maintenance person as a maintenance command. A function of detecting a congestion state and automatically bypassing a route is not provided.
In the VoIP network, in general, all control messages are received regardless a processing ability of a node. Therefore, because of an input of burst traffic, for example, regardless of a processing ability of subscriber accommodation node CL5 11-1, all control messages flow into subscriber accommodation node CL5 11-1 at a time and subscriber accommodation node CL5 11-1 suddenly falls into a congestion state. To recover from such sudden congestion, there is no method other than destroying all the control messages registered in reception queue 16 of subscriber accommodation node CL5 11-1 at a time according to a maintenance command of the maintenance person.
However, when all the control messages are destroyed at a time, even an in-speech call is forcibly disconnected. When a disconnection message registered in reception queue 16 is destroyed, a session cannot be normally closed. This is undesirable because accounting is affected. When subscriber accommodation node CL5 11 of the originating system once falls into a congestion state in this way, a significant problem occurs in that occurrence of a situation undesirable in terms of call control cannot be prevented and congestion propagates to the entire VoIP network, i.e., the entire network of VoIP-C plane 10.
A second problem is in that, because means for controlling traffic among nodes configuring VoIP-C plane 10 for the VoIP service is not provided, a situation in which a large amount of traffic concentrates in specific relay node CL4 12 or the like cannot be prevented and it is highly likely that a congestion state of entire VoIP-C plane 10 is caused.
This is because, since control means (regulating means) concerning a control message for processing request (e.g., a control message for a call setting request such as an INVITE message in an SIP protocol) to be transmitted and received is not provided between subscriber accommodation node CL5 11 and relay node CL4 12 and between relay nodes CL4 12, it is highly likely that processing requests concentrate in a specific node and the node falls into a congestion state. Moreover, in the technique in the past, for example, when control messages are concentratedly originated from plural areas through identical relay node CL4 12, relay node CL4 12 falls into a congestion state. When relay node CL4 12 in VoIP-C plane 10 on the IP network congests, there is a significant problem in that congestion propagates to other nodes connected to relay node CL4 12 and the entire network of VoIP-C plane 10 falls into a congestion state and becomes unstable.
A third problem is that, since regulating means for regulating input traffic from PSTN 50 and other networks is not provided for control of network-to-network connection calls, it is highly likely that traffic concentrates in specific relay node CL4 12 or the like to cause a congestion state of entire VoIP-C plane 10. Moreover, since means for solving a problem of collision of outgoing calls in network-to-network connection is not provided either, it is likely that not only a call setting operation for network-to-network connection calls is hindered but also congestion is caused by repeating exchange of processing requests between networks.
Since the other networks other than the VoIP network such as PSTN 50 cannot grasp a congestion situation of the VoIP network, it is likely that burst-like inflow of traffic into the VoIP network from the other networks occurs. When burst-like inflow of traffic concerning a call setting request (a VoIP outgoing call) from the other networks such as PSTN 50 occurs, appropriate regulation control cannot be realized only by traffic regulation only in VoIP-C plane on the IP network and it is likely that the entire network of VoIP-C plane falls into a congestion state. Therefore, input control means for regulating inflow of input traffic is indispensable for the other networks such as PSTN 50.
A fourth problem is that, since means for automatically regulating input traffic coming in a specific area is not provided, it is highly likely that traffic concentrates in specific subscriber accommodation node CL5 11 or the like on an incoming side to cause a congestion state of entire VoIP-C plane 10. Even when an event in which occurrence of congestion is predicted occurs (e.g., when a concert or a firework display is held or when it is likely that a disaster is caused by a typhoon or the like), VoIP-C plane 10 does not have means for automatically regulating an incoming call concerning the event. Therefore, VoIP calls to subscriber accommodation node CL5 11 in a specific area concentratedly occur and subscriber accommodation node CL5 11 falls into a congestion state. As a result, congestion spreads to respective nodes in entire VoIP-C plane 10.
Moreover, in the technique in the past, when the maintenance person performs maintenance, the maintenance person has to manually input a maintenance command for input regulation for preventing occurrence of congestion due to an event to subscriber accommodation node CL5 1 as an object of maintenance. However, it is likely that the maintenance person omits inputting the maintenance command for input regulation or inputs a wrong command and occurrence of congestion cannot be prevented. After the event ends, the maintenance person needs to manually input a maintenance command for releasing the input regulation. However, it is also likely that the maintenance person omits inputting such maintenance command for releasing the input regulation or inputs a wrong command and omission of release of the input regulation occurs.
In other words, in the technique in the past, when control messages to user terminal 80 of a specific subscriber are concentratedly originated from plural areas, subscriber accommodation node 11 that accommodates user terminal 80 of the subscriber cannot be prevented from congesting. When subscriber accommodation node 11 in VoIP-C plane 10 on the IP network congests, congestion propagates to other nodes connected to subscriber accommodation node 11, the entire network of VoIP-C plane 10 falls into a congestion state and becomes unstable.
Furthermore, the technique disclosed in Patent Document 1 is a technique for controlling, according to congestion to a specific incoming destination (a specific subscriber), density of the number of calls to be equal to or smaller than density of the number of calls corresponding to a threshold set in advance in the respective nodes. The technique is also a technique for regulating the number of calls only on node sides to uniformly control, for the respective nodes configuring the network, the number of calls to the nodes to be equal to or smaller than the threshold regardless of a contracted number of calls of a subscriber and the number of generated calls (generated traffic) in the past. Therefore, the technique is a congestion control method that spoils fairness with respect to the contracted number of calls of the subscriber and the number of generated calls in the past.